Five and six-port circuits are often applied in microwave systems and in wireless communications systems, in particular for use in homodyne receivers. In a five/six-port circuit, there are two input ports and three/four output ports. The input ports of a five/six port circuit are connected to an RF signal and an LO signal, respectively, while the signals at the output ports of the five/six-port circuit are used as input to power detectors, with one power detector for each output port each.
Using the power measured by the power detectors, the in-phase and quadrature components of the base-band signal can be determined. As compared with a receiver which utilizes mixers, a receiver with a five/six port circuit has advantages regarding low DC power consumption, low circuit complexity, low cost, as well as wide bandwidth and re-configurability.
A conventional five/six-port circuit for receivers is often built on a substrate, and is usually a planar circuit which consists of Wilkinson power splitters and 90 degree hybrid couplers, usually designed as microstrip lines on a microwave motherboard. At very high frequencies, for instance, at 60 GHz, such a five/six-port circuit can be integrated with transistors and diodes on MMIC or RFIC chips.
In many microwave applications, existing waveguides are used to connect between a five/six-port circuit designed as a planar circuit and, for example, an antenna or a waveguide duplexer. A waveguide transition, e.g. a microstrip-to-waveguide transition is required for such a connection, which adds to the costs when using a planar five/six port circuit, and which also causes losses at the transition.